1. Field of the Invention
This invention relates to a space saving spare tire which is ready for use in the case of emergency travel on road when a puncture failure or the like is induced in a tire mounted on a vehicle and run on road. The spare tire is normally stored in the vehicle and exclusively used as a spare tire.
2. Description of the Prior Art
In view of saving the space, the above mentioned kind of spare tire is generally classified into a first type spare tire which has an extremely small width and a second type spare tire which is folded and hence is extremely small in volume and appearance.
The first type spare tire which is extremely small widthwise generally has a width on the order of 50% to 80% if compared with a width of a usual tire (which will hereinafter be called as a control tire) and provides extra volume for storage. In addition, the first type spare tire is stored under an inflated condition by applying a high internal pressure on the order of 1.5 to 3.0 times higher than the internal pressure applied to the usual control tire for the purpose of obtaining the same load withstanding ability as that of the control tire. As a result, the first type spare tire has a shape and dimension similar in appearance to a tire for two-wheeled vehicles.
The second type spare tire which is smaller in appearance than the control tire has a volume which is 70% to 80% that of the control tire under its deflated condition and, is stored under this condition. As a result, the second type spare tire can considerably provide extra storage volume. But, when the second type spare tire is used, it must be inflated by means of an inflater to make the tread width, tire width and outer diameter thereof substantially the same as those of the control tire.
Both the first and second type spare tires have good and bad points of their own, but these tires are temporarily used only in the case of emergency. In these spare tires, the tread thickness thereof must be extremely smaller than that of the control tire for the purpose of maintaining cornering performance. In addition, the first type spare tire is used under inflated condition for a long time, so that the tire is subjected to the high internal pressure. As a result, if the first type spare tire is subjected to a cut when the tire is used, the cut easily reaches the carcass because the tread gauge is thin, thereby leaking air through the portion subjected to the cut failure. In general, the carcass cord has an air permeable property. As seen from the above, the first type spare tire has a vital drawback in that the internal pressure becomes decreased and hence the load withstand ability is degraded.
In addition, both the first and second type spare tires are used about one time a year and the internal pressure thereof is not checked. If the internal pressure is low when the spare tire is used, the load withstand ability thereof can not be obtained. As a result, the use of measures of preventing the first type spare tire from leaking air is important.